iMac G5 (iSight) fans constantly running at max speed

[oiuh151]

I have a 17" iMac G5 (iSight) with a 1.9GHz G5 and 512MB of RAM running 10.5.8 with all of the latest security updates. The machine works perfectly fine with the exception of the annoying audible fan noise. From the second I turn the machine on or wake it up from sleep the fans are always at max speed. I've tried resetting the SMU but that didn't change anything and I checked Activity Monitor to see if there was a background process using up a lot of CPU but that wasn't the case. Is there anything else I can do to fix this? I'd rather not re-install the entire OS if it's not guaranteed to fix the issue.

 

[monkeybagel]

From what you have said it does not sound like an OS problem since the fans do this from the moment you turn on the iMac from when you turn it off. If it does it when you still see the Apple logo at startup then you can probably rule the OS out.

I don't believe that machine is a snap to disassemble so perhaps some others will chime in on suggestions.

 

[Hrududu]

Sounds like a thermal sensor is either disconnected or has gone bad. Could also be a bad board. Those are not fun to take apart, so I would first install something like Temperature Monitor and see what readings you're getting. That'll help narrow down where the problem is coming from if its a sensor reading. More than likely you will have to open the machine up though. If you haven't before, then at least it will be a good time to clean it out good. Could be the heatsink and vents are packed with dust and its not ventilating properly.

 

[oiuh151]

I'm not even going to bother if I have to take it apart. I think I'll deal with the fan noise as it's not THAT loud. Thanks though.

 

[Hrududu]

At least take an air compressor and blow out the vents. Those things get clogged up pretty good over years of use.